Jamal is trying to buy something over the phone. He asks his partner to read him his credit card number. However, when he tries to repeat it to the sales clerk on the other end of the line, he can't remember all the numbers.
Jamal is coming up against __________.
a) the decay of numerical memory
b) the extinction of auditory traces
c) George Miller's magic number 7, plus or minus 2
d) the limits of procedural memory